Hypertension (HTN) is a significant health problem in the United States occurring at a higher rate in African Americans than in other racial groups. The frequency of African Americans with Duffy (Fy)-a negative/Fy-b negative red blood cell phenotype is particularly common (80 to 90%). To characterize or correlate a possible genetic link between Fy-a negative/Fy-b negative African-American individuals and HTN, we prospectively performed red blood cell phenotyping for patients and controls from selected hypertension clinics to determine if a correlation does exist in African Americans with Fy-a negative/Fy-b negative red blood cells.